1. Field of the Invention
The invention relates to a display apparatus, more particularly to an image projecting apparatus.
2. Description of the Related Art
As shown in FIG. 1, a conventional image projecting apparatus 1 used in a conventional non-telecentric optical system is for displaying an image onto a screen 16. The conventional image projecting apparatus 1 includes a light-emitting unit 11, a lens unit 12, a reflective light valve 14, and a projection lens 15.
The light-emitting unit 11 includes a plurality of light emitting diodes (LEDs) 111 for providing a light beam, and an integration rod 112 for homogenizing the light beam provided by the LEDs 111. The lens unit 12 includes a condenser 121, and a relay lens 122, which is formed with a notch 123. The lens unit 12 receives the light beam from the integration rod 112, and is capable of adjusting the size of the light beam passing therethrough. Specifically, the size of the light beam passing through the lens unit 12 is adjusted by adjusting the distance between the condenser 121 and the relay lens 122, which is determined by focal lengths thereof. In other words, the size of the light beam passing through the lens unit 12 is controlled by the focal lengths of the condenser 121 and the relay lens 122.
The reflective light valve 14 modulates the light beam exiting the lens unit 12 into an image light. The projection lens 15 receives the image light and projects the image onto the screen 16.
When the conventional image projecting apparatus 1 is to have a low offset, i.e., an offset of between 100% and 110%, the relay lens 122 of the lens unit 12 is required to be disposed in close proximity of the projection lens 15. Therefore, the relay lens 122 is formed with the notch 123 at a lens periphery thereof so as to shorten the distance between the relay lens 122 and the projection lens 15. As a required offset decreases, the size of the notch 123 is increased. However, the non-uniformity of the notch 123 introduces a light-splitting effect, such as that of a prism, into the relay lens 122. As shown in FIG. 2, colors of the image projected on the screen 16 are not uniform due to the light-splitting effect. Specifically, red light, blue light, etc. are visible at corners of the screen 16 when the image should be an all-white image. This results in significant color deviation and low color uniformity near the corners of the image light mainly attributed to the notch 123 in the relay lens 122.